Designing components for plastic extrusion requires understanding how molten material flows, cools, and stabilizes during production. While extrusion is a highly efficient process for producing continuous profiles, designs that do not account for these behaviors can lead to production challenges, dimensional instability, or unnecessary tooling complexity.

Engineers who are more familiar with machining or injection molding often apply similar design assumptions to extrusion, which can create avoidable issues. Recognizing common design mistakes early in the process helps ensure profiles are both manufacturable and reliable in real-world applications.

Inconsistent Wall Thickness

One of the most common design mistakes in extrusion is uneven wall thickness throughout the profile.

When wall thickness varies significantly, material flow through the die becomes unbalanced. Thicker sections retain heat longer, while thinner sections cool more quickly. This can result in:

• profile warping or twisting
• internal stresses within the material
• dimensional inconsistency
• longer setup and stabilization time

Maintaining consistent wall thickness helps promote uniform material flow and improves dimensional stability during production.

If variations are required for strength or function, gradual transitions between sections are preferred over abrupt changes.

Sharp Internal Corners

Sharp internal corners can disrupt material flow and create stress concentration points in the finished profile.

From both a manufacturing and performance standpoint, sharp corners can lead to:

• uneven material distribution during extrusion
• increased internal stress
• reduced long-term durability
• potential cracking under load

Incorporating radii into internal and external corners improves flow through the die and enhances the structural integrity of the final part.

Overly Complex Cross Sections

Extrusion is capable of producing complex profiles, but excessive internal complexity can make the process more difficult to control.

Profiles with intricate geometries, thin webs, or multiple small cavities may result in:

• inconsistent material flow
• difficulty maintaining tolerances
• increased tooling complexity
• longer development and setup time

Simplifying the cross-section where possible helps improve production consistency and reduces tooling challenges.

Balanced designs tend to run more efficiently and produce more stable results.

Designing Without Considering Material Behavior

Different thermoplastics respond differently during extrusion, particularly during cooling and shrinkage.

Material properties such as melt flow, stiffness, and thermal behavior influence how the profile stabilizes after exiting the die.

If material behavior is not considered during design, issues may include:

• unexpected shrinkage
• dimensional variation
• improper fit with mating components
• warping during cooling

Selecting materials based on both performance requirements and extrusion behavior is essential for achieving consistent results.

Waiting Too Long to Involve the Extrusion Manufacturer

A common mistake in extrusion projects is finalizing a design before consulting with the manufacturer.

Extrusion-specific design feedback early in the process can help engineers:

• simplify profile geometry
• adjust non-critical dimensions
• improve manufacturability
• reduce tooling complexity and revisions

Early collaboration often leads to more efficient production and fewer design changes later in the project.

Designing for Manufacturing Success

Successful extrusion profiles are designed with both performance and manufacturability in mind.

Profiles that perform well in production typically include:

• consistent wall thickness
• smooth geometric transitions
• rounded internal and external corners
• practical tolerance expectations
• necessary but controlled complexity

By accounting for how material flows and cools during extrusion, engineers can create profiles that are more stable, cost-effective, and reliable in application.

Working with OEM Engineers

Lincoln Plastics works with OEM manufacturers to produce custom extruded plastic components used in:

• agricultural equipment
• industrial machinery
• infrastructure protection systems
• cord management products

If you're developing a custom extrusion profile and want to discuss manufacturability considerations, our team is always available to help review your design.

Contact us today:
https://www.lincoln-plastics.com/contact-us

Engineer Education Series

This article is part of the Lincoln Plastics Engineer Education Series, which explores key design considerations for plastic extrusion components used in OEM equipment and industrial applications.

Explore the full series:

Engineer Education Series #1:
Designing Plastic Extrusion Profiles – Key Engineering Considerations

Engineer Education Series #2:
Plastic Extrusion Tolerances – What Engineers Should Expect

Engineer Education Series #3: Common Design Mistakes Engineers Make with Plastic Extrusion
Engineer Education Series #4: How Plastic Extrusion Tooling Works
Engineer Education Series #5: Plastic Extrusion vs Injection Molding – When to Use Each
Engineer Education Series #6: Plastic vs Metal Components in Equipment Design
Engineer Education Series #7: Designing Plastic Components for Outdoor Equipment
Engineer Education Series #8: Co-Extrusion vs Single Material Extrusion
Engineer Education Series #9: How Engineers Collaborate with Extrusion Manufacturers
Engineer Education Series #10: Material Selection for Extruded Plastic Parts

Additional Engineering Resources

Engineers interested in exploring extrusion design and manufacturability in greater depth may find the following technical resources helpful:

Society of Plastics Engineers (SPE)
https://www.4spe.org

Pexco – Plastic Extrusion Design Resources
https://www.pexco.com

Dynisco – Extrusion Processors Handbook
https://www.dynisco.com

Plastics Industry Association (PLASTICS)
https://www.plasticsindustry.org

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